full-disclosure - Re: Exploiting sibling domains cookie isolation policy to DoS CDN users

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Message-ID: <20130411160547.GH6549@debjann.fritz.box>
Date: Thu, 11 Apr 2013 18:05:47 +0200
From: Jann Horn <jann@...jh.net>
To: full-disclosure@...ts.grok.org.uk
Subject: Re: Exploiting sibling domains cookie isolation
 policy to DoS CDN users

On Thu, Apr 11, 2013 at 05:01:57PM +0200, Jan Wrobel wrote:
> Hello,
> 
> In short:
> 
> Browsers can be easily cut from any resources hosted on Content
> Delivery Networks that use a domain shared between users, by a visit
> to a malicious site that sets large number of cookies on the common
> prefix of the CDN domain.
> 
> For example, an HTML document on 'foo.rackcdn.com' (visited directly
> or iframed) can set large number of large cookies with a domain
> attribute set to 'rackcdn.com'. This prevents the browser from
> accessing any content on '*.rackcdn.com'. A single site can target
> multiple CDNs at once.
> 
> More detailed writeup:
> http://mixedbit.org/blog/2013/04/11/dos_attack_on_cdn_users.html

Wow, interesting!

CDNs could mitigate this by, instead of resetting connections with lots of headers,
just reading all the cookies and throwing them into the bit bucket instead of keeping
them in RAM, right? That way, there would still be the wasted bandwidth, but
combined with the Google approach, it should work fine, right? If the client sends too
many headers, just ignore everything until you reach \n\n, then send back the error
script?

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